Learn how to write a C program that can effectively identify and print all happy numbers up to a specified limit, N, with our simple and easy-to-follow tutorial.

## What is a Happy Number?

A number is considered a happy number if it reaches 1 after being repeatedly replaced by the sum of the squares of its digits. For example, 23 is a happy number because:

```
2^2 + 3^2 = 13
1^2 + 3^2 = 10
1^2 + 0^2 = 1
```

## C Program to Print All Happy Numbers Till N

Here's a C program that prints all happy numbers up to N:

```
// Include standard I/O and boolean header files
#include <stdio.h>
#include <stdbool.h>
// Function to check if a number is a happy number
bool isHappy(int num) {
int sum, digit;
// Loop until num becomes 1 or 4
while (num != 1 && num != 4) {
sum = 0;
// Find the sum of the squares of the digits
while (num > 0) {
digit = num % 10;
sum += digit * digit;
num /= 10;
}
num = sum;
}
// Return true if num becomes 1, otherwise false
return (num == 1);
}
// Main function
int main() {
int N, i;
// Ask the user for the upper limit
printf("Enter the value of N: ");
scanf("%d", &N);
// Print all happy numbers up to N
printf("Happy numbers till %d are: ", N);
for (i = 1; i <= N; i++) {
if (isHappy(i)) {
printf("%d ", i);
}
}
printf("\n");
return 0;
}
```

Program Output:

```
Enter the value of N: 50
Happy numbers till 50 are: 1 7 10 13 19 23 28 31 32 44 49
```

Code Explanation:

The above program is split into two main parts: the `isHappy`

function and the `main`

function:

- The
`isHappy`

function takes an integer and returns whether it's a happy number or not. It uses a`while`

loop to repeatedly square and sum the digits until the sum is either 1 (happy) or 4 (not happy). - The
`main`

function asks for an upper limit " and iterates from 1 to the " , calling`isHappy`

for each number. If the number is happy, it gets printed.

## Conclusion

In this tutorial, you were guided through a C program that helps you identify and print happy numbers up to a specific numerical value, N. The program uses fundamental C programming concepts such as loops and functions, making it easily understandable and accessible to beginners. By following the instructions and implementing the code, you can gain a deeper understanding of these concepts and apply them to real-world scenarios.